Electronic paper (E-paper) is a display technology designed to mimic the appearance of ordinary ink on paper. A particle-based display, such as an electrophoretic display, is widely used in E-papers. Particle-based displays comprise a plurality of independently addressable display cells arranged in an array, wherein each display cell comprises a plurality of pigment particles that are held between a pair of opposing, spaced-apart electrodes. An electrophoretic display can be a powder type display in which particles of different polarities and contrast colors are suspended in a gaseous medium in the display cells as shown in FIG. 1A. An electrophoretic display can be a microcapsule type display in which particles of different polarities and contrast colors are enclosed in a plurality of microcapsules as shown in FIG. 1B. An electrophoretic display can also be a microcup type display in which charged particles are dispersed in a contrast-colored fluid as shown in FIG. 1C.
In a display apparatus operated in the in-plane switching mode, both electrodes are on the same plane or substrate. In a display apparatus operated in the top-down switching mode, the two electrodes are on different (top and bottom) substrates. In all cases, at least one of the two substrates is transparent so that the state of the particles can be viewed through the transparent substrate. When a voltage difference or an electrical field is imposed between the first and second electrodes, the pigment particles migrate to the electrode which has opposite polarity to the pigment particles. Thus, changes in the color or shade displayed through the transparent electrode are facilitated by selectively changing the polarities of the electrodes.
When the pigment particles migrate to and contact the electrode with the polarity opposite to the pigment particles, electrons may gradually leak through the contact surface even after the power is turned off. Thus, the longer the particles contact the electrode, the less charge density (charge per unit weight, Q/W) remains on the particle surface and the more difficult it is to re-drive the pigment particles by electric field.